/Engine/Source/Runtime/ApplicationCore/Public/GenericPlatform/GenericPlatformInputDeviceMapper.h
Remap aFPlatformUserIdto the legacy platform LocalUserIndex (often the same as ControllerId). This is useful in cases where the input device id is not needed.
A valid platform user index, or INDEX_NONE
virtual int32 GetUserIndexForPlatformUser ( [FPlatformUserId](API\Runtime\Core\Misc\FPlatformUserId) UserId )